1. Field of the Invention
The present invention relates to an apparatus for judging an optical disk, and in particular to an improved apparatus for judging an optical disk which makes it possible to judges the type of an optical disk by detecting a phase difference of E and F signals which are two sub-beams detected by an optical pick-up apparatus.
2. Description of the Conventional Art
Generally, the CD (Compact Disk) is formed by coating a writing medium on one side of the same made of an aluminum. This CD is widely used as a storing medium by emitting a laser beam on the side into which the data are written for thereby reproducing the written data.
As the storing medium which is implemented by emitting a laser beam into the side of the same into which the data are written, a DVD (Digital Video Disk) is known. This DVD has a large storing capacity capable of storing few giga bytes of data including motion pictures. In the future, the DVD will be used for storing the digital data compressed based on MPEG-II and for a high resolution and quality multimedia medium which may run for more than two hours.
FIG. 1 is a view illustrating a comparison between the data written into the conventional CD and DVD.
As shown therein, the disk information is obtained from a protruded surface which is called a pit. In the case of the CD, the minimum size of the pit is N, and in the case of the DVD, the minimum size of the pit is N'(an example of relative distance between pits is shown as M). As a result of the comparison therebetween, since the pit of the CD is smaller by half than the same of the DVD, the DVD is capable of storing more data compared to the CD.
The thickness of the CD is the thickness as the same of the DVD. Thus the fact that the thicknesses of the CD and DVD are the same means that the distance between the disk surface and the reflection surface is same in the CD and DVD, respectively.
Therefore, the optical disk reproducing apparatus with a DVD reproducing function has also a CD reproducing function. In this optical disk reproducing apparatus, a controller provided in the optical disk reproducing apparatus judges whether the optical disk mounted is a CD or DVD, so that the operation of the system is controlled based on the type of the optical disk mounted in the deck of the system.
However, in the optical disk reproducing apparatus with the DVD reproducing function, in the case that an optical disk is mounted into the deck, the type of the optical disk mounted in the deck of the system is judged by reproducing a read-in region of the optical disk. In this case, long read-in time is required for reproducing the read-in region for judging the disk type between the CD and DVD.